How to Configuring Cisco IOS Software first you will want to configure every switch in an Enterprise network, even though the switches will forward traffic even with default configuration. This section covers the essential configuration processes, including the concept of a configuration file and therefore the locations during which the configuration files are often stored. Although this section focuses on the configuration process, and not on the configuration commands themselves, you must know all the commands covered during this chapter for the exams, additionally to the configuration processes. Configuration mode is another mode for the Cisco CLI, almost like user mode and privileged mode.
User mode lets you issue non-disruptive commands and displays some information. Privileged mode supports a superset of commands compared to user mode, including commands which may disrupt switch operations. However, none of the commands in user or privileged mode changes the switch’s configuration. Configuration mode accepts configuration commands —commands that tell the switch the details of what to do and the way to do it. Figure 6-7 illustrates the relationships among configuration mode, user EXEC mode, and privileged EXEC mode.
Commands entered in configuration mode update the active configuration file. These changes to the configuration occur immediately every time you press the Enter key at the end of a command. be careful once you enter a configuration command!
Configuration Submodes and Contexts
Configuration mode itself contains a multitude of commands. to assist organize the configuration, IOS groups some sorts of configuration commands together. to do that, when using configuration mode, you progress from the initial mode—global configuration mode—into subcommand modes. Context-setting commands move you from one configuration subcommand mode, or context, to a different . These context-setting commands tell the switch the subject about which you’ll enter the next few configuration commands. More importantly, the context tells the switch the subject you care about immediately , so once you use the ? to urge help, the switch gives you help that topic only.
Also Read : What are the LAN Switching Concepts
The best way to find out about configuration submodes is to use them, but first, take a look at these upcoming examples. as an example , the interface command is one among the foremost commonly used context-setting configuration commands. for instance , the CLI user could enter interface configuration mode by entering the interface FastEthernet 0/1 configuration command. asking for help in interface configuration mode displays only commands that are useful when configuring Ethernet interfaces. Commands used in this context are called subcommands— or, during this specific case, interface subcommands. once you begin practicing with the CLI with real equipment, the navigation between modes can become natural. For now, consider Example 6-4, which shows the following :
- Movement from enable mode to global configuration mode by using the configure terminal EXEC command
- Using a hostname Fred global configuration command to configure the switch’s name
- Movement from global configuration mode to console line configuration mode (using the line console 0 command)
- Setting the console’s simple password to hope (using the password hope line subcommand)
- Movement from console configuration mode to interface configuration mode (using the interface type number command)
- Setting the speed to 100 Mbps for interface Fa0/1 (using the speed 100 interface subcommand)
- Movement from interface configuration mode back to global configuration mode (using the exit command)
The text inside parentheses within the command prompt identifies the configuration mode. for instance , the primary command prompt after you enter configuration mode lists (config), meaning global configuration mode. After the road console 0 command, the text expands to (config-line), meaning line configuration mode. whenever the command prompt changes within config mode, you’ve got moved to a different configuration mode. Table 6-4 shows the foremost common command prompts in configuration mode, the names of these modes, and therefore the context-setting commands wont to reach those modes.
You should practice until you become comfortable moving between the various configuration modes, back to enable mode, then back to the configuration modes. However, you’ll learn these skills just doing labs about the topics in later chapters of the book. For now, Figure 6-8 shows most of the navigation between global configuration mode and therefore the four configuration submodes listed in Table 6-4.
You really should stop and try navigating around these configuration modes. If you’ve got not yet selected a lab strategy, spin the DVD within the back of the book, and install the Pearson Sim Lite software. It includes the simulator and a few of lab exercises. Start any lab, ignore the instructions, and just get into configuration mode and move around between
the configuration modes shown in Figure 6-8. No set rules exist for what commands are global commands or subcommands. Generally, however, when multiple instances of a parameter are often set during a single switch, the command wont to set the parameter is probably going a configuration subcommand. Items that are set once for the whole switch are likely global commands. for instance , the hostname command may be a global command because there’s just one hostname per switch. Conversely, the speed command is an interface subcommand that applies to every switch interface which will run at different speeds, so it’s a subcommand, applying to the actual interface under which it’s configured.
Storing Switch Configuration Files
When you configure a switch, it must use the configuration. It also must be ready to retain the configuration just in case the switch loses power. Cisco switches contain random-access memory (RAM) to store data while Cisco IOS is using it, but RAM loses its contents when the switch loses power or is reloaded. To store information that must be retained when the switch loses power or is reloaded, Cisco switches use several sorts of more permanent memory, none of which has any moving parts. By avoiding components with moving parts (such as traditional disk drives), switches can maintain better uptime and availability.
The following list details the four main sorts of memory found in Cisco switches, also because the commonest use of every type:
- RAM: Sometimes called DRAM, for dynamic random-access memory, RAM is used by the switch even as it’s used by the other computer: for working storage. The running (active) configuration file is stored here.
- Flash memory: Either a chip inside the switch or a removable memory card, flash memory stores fully functional Cisco IOS images and is that the default location where the switch gets its Cisco IOS at boot time. flash memory can also be wont to store the other files, including backup copies of configuration files.
- ROM: ROM (ROM) stores a bootstrap (or boothelper) program that’s loaded when the switch first powers on. This bootstrap program then finds the complete Cisco IOS image and manages the process of loading Cisco IOS into RAM, at which point Cisco IOS takes over operation of the switch.
- NVRAM: Nonvolatile RAM (NVRAM) stores the initial or startup configuration file that’s used when the switch is first powered on and when the switch is reloaded. Figure 6-9 summarizes this same information during a briefer and more convenient form for memorization and study.
Cisco IOS stores the gathering of configuration commands during a configuration file. In fact, switches use multiple configuration files—one file for the initial configuration used when powering on, and another configuration file for the active, currently used running configuration as stored in RAM. Table 6-5 lists the names of those two files, their purpose, and their storage location.
Essentially, once you use configuration mode, you modify only the running-config file. this means that the configuration example earlier during this chapter (Example 6-4) updates only the running-config file. However, if the switch lost power right then example, all that configuration would be lost. If you would like to stay that configuration, you’ve got to repeat the running-config file into NVRAM, overwriting the old startup-config file. Example 6-5 demonstrates that commands utilized in configuration mode change only the running configuration in RAM. the instance shows the following concepts and steps:
Step 1. the instance begins with both the running and startup-config having the same hostname, per the hostname hannah command.
Step 2. The hostname is modified in configuration mode using the hostname Jessie command.
Step 3. The show running-config and show startup-config commands show the very fact that the hostnames are now different, with the hostname jessie command found only within the running-config.
Copying and Erasing Configuration Files
The configuration process updates the running-config file, which is lost if the router loses power or is reloaded. Clearly, IOS must provide us how to repeat the running configuration so that it’ll not be lost, so it’ll be used the next time the switch reloads or powers on. as an example , Example 6-5 ended with a special running configuration (with the hostname jessie command) versus the startup configuration. In short, the EXEC command copy running-config startup-config backs up the runningconfig to the startup-config file. This command overwrites the present startup-config file with what’s currently within the running-configuration file. additionally , in lab, you’ll want to only get rid of all existing configuration and begin over with a clean configuration. to try to to that, you’ll erase the startup-config file using three different commands:
write erase
erase startup-config
erase nvram:
Once the startup-config file is erased, you’ll reload or power off/on the switch, and it’ll boot with the now-empty startup configuration. Note that Cisco IOS doesn’t have a command that erases the contents of the runningconfig file. To filter out the running-config file, simply erase the startup-config file, then reload the switch, and therefore the running-config are going to be empty at the top of the method .
Questions related to this topic
- How do I load a config file into a Cisco switch?
- Which part of the syntax is represented by running config?
- How do I see running config on a Cisco switch?
- How do I copy the running configuration to the startup configuration?
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